It is estimated that approximately half of HIV-infected individuals in the United States are over 50 years of age. Aging of the HIV-infected population has linked alterations in immune responses associated with age and the immunologic consequences of chronic HIV infection. This intersection of HIV and aging will influence host defense against infection and response to vaccines. As a result, understanding the nexus of HIV-associated immune activation and immunosenescence takes on particular urgency. We will leverage insights from our published and ongoing studies on the effects of aging on dysregulated innate immune pattern recognition receptor (PRR) function, a novel population of pro-inflammatory IL-7 receptor alow effector memory (EM) CD8 T cells that are expanded in HIV-negative older adults, and on expansion of EM CD8 T cells in older HIV-positive adults. We have also elucidated gene expression and immunologic signatures of influenza vaccine response in young and older HIV-negative adults. These findings position us to illuminate the effects of aging and HIV infection on innate and adaptive immune function, particularly following influenza vaccination. To address these questions, we have assembled an interdisciplinary group of investigators with expertise in the study of aging of the innate and adaptive human immune systems, and in HIV immunology, biology and clinical care. Our overarching hypothesis is that the pro-inflammatory environment associated with age and with suppressed HIV infection potentiates immunosenescence in older adults with HIV disease. To test this hypothesis, we will enroll young (age 21-35) and older (age over 65) adults with HIV infection receiving high-dose influenza vaccine. We will employ state of the art methods including multichannel mass cytometry on whole blood to assess development and activation of major populations (e.g. monocytes, dendritic cells, NK cells, lymphocytes, neutrophils), including novel studies of platelets pre- and post-vaccine. We will evaluate innate immune PRR function (including Toll-like and NOD-like receptor family members), where we previously found age-associated alterations in cytokine production and costimulatory protein expression that were related to influenza vaccine response. We will also study T cell responses to in vitro vaccine antigen stimulation, including the IL-7 receptor alow EM CD8 T cell subset. Statistical modeling will include clinical and functional covariates (e.g. CD4+ T cell count, estimated duration of HIV disease and of ART, medical co-morbidities, medication use, functional status). Finally, we will derive gene expression signatures of influenza vaccine response in young and older adults with HIV disease, and compare these to those we previously identified in HIV-negative adults. We will employ state of the art analytic methods to integrate gene expression and immunologic data to obtain a comprehensive view of the human immune response in the context of age and immune suppression. These studies ultimately are aimed at identifying pathways amenable to pharmacologic targeting to improve immune and vaccine responses in older (and young) adults with HIV disease.